A light emitting device utilizing light emission from an electroluminescent element (light emitting element) attracts attention as a device for displaying or lighting.
As the light emitting element used in the light emitting device, a light emitting element having a structure in which a layer containing a luminescent compound is interposed between a pair of electrodes is well known.
In such a light emitting element, one electrode functions as an anode, and the other electrode functions as a cathode. Holes injected from the anode side and electrons injected from the cathode side recombine to form excited state molecules, and when the molecules return to a ground state, they emit light.
By the way, the reduction of power consumption is highly required especially in a display device incorporated in various information-processing devices which has been rapidly developed these days. In order to achieve the requirement, the reduction of driving voltage of the light emitting element is being attempted. In consideration of commercialization, the increase of the lifetime of the light emitting element is important as well as the reduction of the driving voltage, and in order to achieve this, the light emitting element is being developed.
For example, in Reference 1 (Japanese Patent Laid-Open No. H9-63771), a technique of reducing driving voltage of a light emitting element by using metal oxide having a high work function such as molybdenum oxide as an anode is disclosed. Further, with the technique disclosed in Reference 1, an effect of increasing lifetime can be obtained.
However, since molybdenum oxide is easy to be crystallized, the number of malfunctions of the light emitting element due to the crystallization cannot be reduced sufficiently. In other words, since molybdenum oxide is crystallized to form a projection portion and loses flatness, a short circuit easily occurs and there is a problem of easily causing malfunctions of the light emitting element.